I'm trying to decide on 4 tires for a tandem axle with a 520 sitting on it. I don't know whether to stay with Marathons, or go with the Cooper tire, which is an automotive tire. The size of the Marathon is 215 75 14, the Cooper is 215 70 14. Any problem in the size difference? I know BCB runs the Cooper, so in theory, so should my Ranger Trail. Any thoughts? Thanks for any help.